;-------------------------------------------------------------LICENSE--------------------------------------------------------------;
;                                                                                                                                  ;
;The MAP code is written in Fortran language for magnetohydrodynamics (MHD) calculation with the adaptive mesh refinement (AMR)    ;
;and Message Passing Interface (MPI) parallelization.                                                                              ;
;                                                                                                                                  ;
;Copyright (C) 2012                                                                                                                ;
;Ronglin Jiang                                                                                                                     ;
;rljiang@ssc.net.cn                                                                                                                ;
;585 Guoshoujing Road. Pudong, Shanghai, P.R.C. 201203                                                                             ;
;                                                                                                                                  ;
;This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License         ;
;as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.             ;
;                                                                                                                                  ;
;This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of    ;
;MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.                        ;
;                                                                                                                                  ;
;You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software     ;
;Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.                                                   ;
;                                                                                                                                  ;
;-------------------------------------------------------------LICENSE--------------------------------------------------------------;

function dif,cood

ncood=n_elements(cood)

dcood=(shift(cood,-1)-shift(cood,1))/2
dcood[0]=dcood[1]
dcood[ncood-1]=dcood[ncood-2]

return,dcood

end
